1. Field of the Invention
The present invention relates to an electrophotographic copying apparatus equipped with a magnification changing copying function, and more particularly to an electrophotographic copying apparatus provided with an original document size detecting means and a selecting means of magnification changing elements so that either the size of copy paper to be copied or the magnification ratio is automatically selected or adjusted.
2. Description of the Related Art
There have been many kinds or types of electrophotographic copying machines introduced into the market which are able to copy with changing magnification ratios. The magnification changing copying function as referred to above is such that an image of an original document placed on an original document platform is enlarged or reduced in size for copying in accordance with the predetermined magnification ratio. It is necessary, therefore, in order to effectively work the magnification changing copying function, to determine various elements or factors requiring the change of the magnification ratio which comprise the size of an original document, the magnification ratio and the size of copy paper to be copied on.
For example, one of the conventional electrophotographic copying machines has an original document size detection device provided below the original document platform which automatically detects the size of the original document placed on the platform, so that the operating steps required of an operator necessary to input the above-described magnification changing elements are simplified. Further, such an electrophotographic copying machine has also been proposed equipped with a selecting device of various magnification changing elements for calculating and selecting a proper magnification ratio or a proper size of copy paper based on the size of the original document detected by the original document size detecting device and, the size of the copy paper or the magnification ratio inputted by the operator.
However, in the prior art electrophotographic copying machines, in the case where the size of the original document or of the copy paper is set less than half the size of the largest paper usable for the copying machine, larger and smaller two magnification ratios may become selectable if the direction of placement of the original document or that of supply of the copy paper is changed, and there may develop the case where the image forming area is larger than the size of the copy paper.
More specifically, in FIG. 5, there is seen an original document platform having A3 for the largest size of paper to be copied thereon. If an original document of A4 size is to be placed on the platform, it is possible for the original document to be placed on the platform with its longitudinal direction crossing the exposure scanning direction (an arrow A) or parallel to the exposure scanning direction. When this original document of A4 size is to be copied on copy papers of A3 size, in the case where the longitudinal direction of the original document is brought into parallel relation to the exposure scanning direction, that is, in the case of A4R, the magnification ratio of 1.41 is selected by the selecting device of the various magnification changing elements. On the contrary, in the case where the longitudinal direction of the original document is placed in the direction crossing the exposure scanning direction the magnification ratio of equal size is selected and accordingly, the image of A4 size is formed on half of the copy paper of A3 size, resulting in such inconvenience that the magnification changing copying function cannot be effectively utilized. Moreover, in the case where the longitudinal direction of the original document is placed in the direction crossing the exposure scanning direction and at the same time, the operator selects a magnification ratio for an enlarged copy, there is a possibility that the image becomes larger than the copy paper selected by the selecting device by the use of the size of the original document and the magnification ratio, also resulting in the inconvenience that the magnification changing copying function cannot be effectively utilized.